It is increasingly common for wireless communication systems to use digital modulation schemes such as Code Division Multiple Access (CDMA) to establish physical communication channels between a base station and one or more mobile subscriber units. The base station is typically a computer controlled set of transceivers that are interconnected to a land-based public switched telephone network (PSTN). The base station includes an antenna apparatus for sending radio frequency signals to the mobile subscriber units, a direction known as the forward link. The base station antenna is also responsible for receiving reverse link radio frequency signals transmitted from each mobile unit.
Each mobile subscriber unit also contains an antenna apparatus for the reception of the forward link signals and for transmission of the reverse link signals. A typical mobile subscriber unit is a digital cellular telephone handset or a personal computer coupled to a cellular modem. In CDMA cellular systems, multiple mobile subscriber units may transmit and receive signals on the same frequency but with different codes, to permit detection of signals on a per unit basis.
The most common type of antenna used to transmit and receive signals at a mobile subscriber unit is a mono- or omni-pole antenna. This type of antenna consists of a single wire or antenna element that is coupled to a transceiver within the subscriber unit. The transceiver receives reverse link signals to be transmitted from circuitry within the subscriber unit and modulates the signals onto the antenna element at a specific frequency assigned to that subscriber unit. Forward link signals received by the antenna element at a specific frequency are demodulated by the transceiver and supplied to processing circuitry within the subscriber unit.
A second type of antenna which may be used by mobile subscriber units is described in U.S. Pat. No. 5,617,102. The system described therein provides a directional antenna comprising two antenna elements mounted on the outer case of a laptop computer. The system includes a phase shifter attached to the two elements. The phase shifter may be switched on or off in order to effect the phase of signals transmitted or received during communications to and from the computer. By switching the phase shifter on, the antenna transmit pattern may be adapted to a predetermined hemispherical pattern which provides transmit beam pattern areas having a concentrated signal strength or gain. The dual element antenna directs the signal into predetermined quadrants or hemispheres to allow for large changes in orientation relative to the base station while minimizing signal loss.
A third type of antenna which may be used by mobile subscriber units includes multiple antenna elements and a like number of adjustable phase shifters, each respectively coupled to one of the antenna elements. The phase shifters are independently adjustable (i.e., programmable) to affect the phase of respective reverse link signals to be transmitted from the subscriber unit on each of the antenna elements. The antenna apparatus acts as a beamformer for transmission of signals from the subscriber unit and acts as a directive antenna for signals received by the subscriber unit.
While the antenna of the subscriber units allow a user mobility, the antenna apparatus itself can have several shortcomings. Without a protective covering, the antenna elements of the antenna apparatus would be exposed to dust and dirt from the environment. Similarly, a lack of a protective covering or housing for the antenna would expose the antenna to the risk of breakage during transport. Another shortcoming involves the situation where an antenna apparatus unit has multiple antenna which are each fairly long. Such antenna apparatus are not especially convenient for the mobile user to set up and tear down.